At present, it is inevitable that civil engineering work, construction work, etc., are required to be performed on soft ground, such as reclaimed land, in order to promote efficient use of limited space. Such soft ground is usually dehydrated by scattering a hardening agent so that the soil is regenerated. Further, when water supply or drainage works or gas pipe laying works are carried out, the ditches for laying the pipes are usually refilled, using soil which has been dug by construction machines such as hydraulic shovels.
However, watery clay or sticky soil, which has been dug and stirred up by hydraulic shovels or the like, cannot hold itself. Therefore, soil which is not usable for filling the ditches has to be relocated using dump tracks.
Japanese Patent Laid-Open Publication 54-58901 has proposed a soil improving method in order to overcome these problems. According to the publication, a predetermined amount of sticky soil, which is not applicable to filling ditches, is sequentially supplied, contacted with a soil improving agent having wet-hard characteristics in a predetermined ratio, and then crushed and mixed. The publication also discloses a soil improving machine, which comprises a conveyor for relocating sticky soil which is not usable for filling ditches, a cut screw for slicing the unusable soil into layers having a predetermined thickness and for removing surplus soil at an appropriate position, a device for adding a predetermined amount of wet-hard type soil improving agent to a preset amount of soil carried on a conveyor, and a crusher for crushing and mixing the soil and the soil improving agent.
The foregoing soil improving machine, however, crushes and mixes soil and soil improving agent using only one crushing cutter; thus it is difficult to efficiently mix the soil with the soil improving agent.
An impact crushing/mixing machine for dug soil is known in Japanese Patent Publication 4-9586. This machine includes rotary strikers, flexible crushing plates, and a casing which houses a plurality of crushing pieces coupled to the flexible crushing plates, at least a pair of elastic members extending along the flexible crushing plates, and a support for coupling flexible crushing plates in the vicinity of the elastic members.
However, such an impact crushing/mixing machine has a problem in that it cannot crush and mix sticky soil but only deform it.
There is another problem in that a lot of dust is generated when soft ground is dried by hardening agent. There is a further problem in that when a construction site is narrow, construction machines, such as vehicles for scattering hardening agent and vibrating rollers for ramming the land, etc., cannot be simultaneously introduced there. Still further, construction cost is increased when a number of construction machines are used according to conventional methods.